Luminescent material



Patented Aug. 20, 1940 UNITED v STATES PATENT v foFFlcE f 2,21z,zo9

Humboldt w. Iieverenz, South Orange, N. 1., as-

' signer to Radio Corporation oi. America, a corporation oi. Delaware No Drawing.

application March 19,

Divided and this application June 9, 1939, Serial No. 278,327

' This application is a division of application Serial No. 131,862, filed March 19, 1937, and entitled Luminescent ,material which issued as Patent No. 2,171,145 inv August, 1939.

This invention relates to a process forsynthesizing luminescent materials and, in particular,

is directed to' producing luminescent materials of improved properties and with the further advantage that the spectral luminosity of the resultant material may be predetermined at the time of manufacture.

Luminescent materials, particularly those adapted to become excitedunder theinfluence of electric bombardment such as cathode ray beam and tubes used for television, oscillographs and allied uses have been known for some time by the commonly used luminescent materials known to the workers in the art, and always had the drawback of lacking consistent reproduction so of their characteristic properties within close limits. For example, batches of luminescent material obtained at different times hithertoiore from natural sources or from those synthesized in laboratories or factories would show diflerent a spectral emission characteristics due to an inability to produce materials having uniform tially invariant spectral distribution, and a wide.

band spectral distribution. It will be readily appreciated, therefore, that this new lumines- 0 cent material has many qualities which make it extremely desirable for use in cathode ray tubes,

7 for example.

My present invention relates to a process for producing and/or preparing a luminescent ma- 4 terial possessing the above characteristics. In

. addition, the process of manufacture results in the production of a' luminescent material wherein the very valuable property of controlled spectral emission is established by the process of manufacture. In the past, luminescent mate-- rials have had a characteristic spectral distri-- bution which was solely a function of the elements making up the material and in this respect the color of the emitted luminosity under cathode ray bombardment was fixed. By my invention I have developed a luminescent material wherein it is possible to control the color oi'the emitted light over a wide spectral range, by merely changing the proportions w of the elements entering into the compositional 4 Claims. (a. 250-81) the final material and/or the final heating temperatures of the material.

Accordingly, it' is one of the purposes of my invention to provide a luminescent material whose spectral emission may be modified from 5 one end of the spectrum to the other in all the intermediate wave lengths thereof by changing the proportions of the material entering into the synthesis of the finally prepared luminescen material. I r a 10 Likewise it is one of the purposes of my invention to provide a luminescent material whose spectral emissionmay be modified by controlling the temperature and duration of the heating of the luminescent product during its preparation. 16.

A further object of my invention is to shift the emission spectrum from the violet end toward longer wave lengths up to and including the red end by isomorphic mutual replacements in the crystal lattice of the luminescent mate- .0. rial.

Another object 01' my invention is to prepare a material which will emit light of high intensity under cathode ray bombardment.

A still further object of my invention is to provide a process for synthesizing a luminescent material with substantially invariant spectral distribution with regard to length of time of cathode ray bombardment.

Another object of my invention is to prepare a so material which" will produce the effect of emitting white light under high .intensity cath- I provide a process whereby improved luminescent materials may be prepared with minimum expense but, nevertheless possess the advantage of uniformly superior response characteristics. 5

Other. objects and advantages of myinvention will be immediately apparent to those skilled in the art upon reading the following description of. my invention.

a The luminescent-material resulting from my ,invention is a-crystalline structure comprising zinc ortho-silicate and zirconium ortho-silicate,

' activated by manganese, and may incorporate an excess of silicon dioxide held in the crystalline formation of the material. It should be clearly v understood that this is not a mixture of zinc ortho-silicate and zirconium ortho-lsilicate in the usual chemical sense, but actually is a homogeneous crystal comprising manganese zinc .ortho-silicate and zirconium ortho-sillcate in a single crystal latticestructure or where an excess amount of silicon dioxide is used, as will be described later, wherein the zinc and zirconium silicates and manganese are held in a single lattice structure. In this material the ratio between the zinc ortho-silicate and the zirconium ortho-silicate may be varied from 10,000 to 1 to 1 to 10,000. Thus a formula which is descriptive of a luminescent materialpossessing the above outlined characteristics may be expressed as i'ollowsi In this formula the variable :0 and u may be such that :r/y may be varied from 10,000/1 to '1/10,000. This formula. is descriptive of where the amount of silicon dioxide is such to give the exact ortho-silicate proportions. However, where these proportions are not followed and an excess or insufllcient amount of silicon dioxide is used, then the following formulais descriptlve of the luminescent material:

Here the ratio between it and 22 may be varied over extremely wide limits such as, for example,

- as indicated above and w may have a range from i: to 5 times n+1).

The composition may also be written as u(ZnO) v(ZrOz) 217(8102) 1(MDOx) indicating that the manganese activator may be in the form of an oxide, and to further indicate that the formula does not mean a chemical composition in the usual sense which. chemical formulas indicate. It will be appreciated, of

. course, that the colon indicates that the substances following the colon are present in very small quantities and constitute the activator.

Such terminology has already been used in the art and serves to indicate that the activator is held in such close physical bondage that breaking down the substance even into microscopic particles still gives the substance substantially the same properties .as it has with microscopicagsregates so'that for all intentsand purposes it might be called a quasi-chemical compound.

The amount of silicon dioxide may be varied from amounts less than needed for ortho-proportions to 100% or greater than the ortho-proportions. In practice it has been determined that the amount of silicon dioxide may be varied from a lower limit of approximately 20% to an upper limit of approximately 500% of the amount which would be necessary, calculated on the basis a of ortho-proportions. The amount of manganese While the amount otmanganese may be varied may likewise be varied within wide limits-tor example, between values of 0.1 molal to 0.00001 molal with respect to the total cation molality.

between these wide limits so as to control, in part, the spectral response, it is found that when the amount of manganese is approximately 0.006 molal, themaximum efiiciency in conversion or energy to light by the luminescent material is obtained. Should this proportion of manganese not give the required spectral response, the spectral response maybe shifted by other meanssuch as the heat treatment or changing the proportions of the zinc oxide, zirconium dioxide, or

silicon dioxide.

' If it is desired, the spectral response may be shifted or controlled by substitution of titanium, hafnium and/or thorium in whole or in part for the zirconium. V

It may be pointed out at this point that berylaeiaaoe lium may be substituted in part or in whole for zinc in the above formula in accordance with the method and means described in my co-pending application entitled Luminescent materials Serial No. 66,453,.filed'September 29, 1936 which issued as Patent No. 2,118,091 in May, 1938. In fact, any metal in the second vertical group of the periodic system,'whose oxide does not decompose below 700 C. can be substituted in part or in whole for zinc. The metals thus falling within this group, in addition to beryllium, would be magnesium, cadmium, calcium, strontium and barium.

Likewise, germanium may be substituted for silicon in part or in whole, as explained and described in my co-pending application entitled Process for synthesizing luminescent materials, Serial No. 707,866, filed January 23, 1934. Thus it appears that a metal in the first sub-group of the fourth vertical group of the periodic system having an ionic radius lying between 0.3 A. and 0.7 A.-

may be used.

The steps in the process of mixing,precipitating, heating, and. finally grinding the luminescent material as in a ball-mill, for example, have already been described in detail by my co-pending application Serial No. 707,866 filed January 23, 1934, in which I have described the preparation of a manganese activated ortho-silicate. The essential differences between the preparation of this material and that described in the above mentioned copending application is that in the preparation of my manganese activated zinc zirconium orthosilicate material, exceedingly pure zinc nitrate and zirconium nitrate solutions are added to very finely divided silicon dioxide in suspension as, for example, colloidal silicon dioxide, in proper proportion, as specified by the above mentioned conditions to be met with regard to a: and 11, in contradistinction to the use only of zinc nitrate. The mixture is heated and stirred and when brought to a boil, there is added very slowly and carefully with plenty of agitation saturated ammonium carbonate solution of great purity and in suflicient quantity to precipitate the metallic salts as carbonates on the finely divided silicon dioxide. The contents of the beaker are then evaporated with stirring to. dryness and then heated by any appropriate manner to red heat. The contents are then allowed to cool and are ground and mixed with a quartz rod. The resultant product is then placed in a quartz crucible and a suitable quantity of manganese nitrate solution of the greatest purity obtainable is added, the exact quantity ranging between 0.1 and 0.00001 molal with respect to the total cation molality depending on the actual spectralemission distribution desired.

Quartz distilled water is then added to the amount to make the mixture thoroughly wet. The crucible is then heated and the contents thereof stirred until brought to a boil, whereupon concentrated ammonium carbonate is added to precipitate the manganese, in the form of manganese carbonate upon the previously precipitated carcomponents may be precipitated at once and so save the extra step in the process.

The contents of this crucible are then evaporated with stirring to dryness and upon cooling the contents are ground with a quartz rod. The contents are then transferred to a covered crucible and heated to between 700 and 1600 C. in an electric furnace, for example. It has been found by experience that the optimum temperature lies between 11001500 C. and the heating time is preferably on the order of an hour. The final product is a lightly fritted powder or a fused mass which gives intense cathodo-luminescence, whose color depends upon the actual ratio between the zinc ortho-silicate and zirconium ortho-silicate..

For a ratio of unity between these two materials and under high intensity electron bombardment, the emitted light appears white. It will be appreciated, of course, that by changing the ratio of the zinc ortho-silicate to the zirconium orthosilicate, the color may be shifted from the normal green blue of pure manganese activated zinc ortho-silicate toward the red end of the spectrum to give a more pleasing color. Other changes in the spectral emission spectrum may be had by changing the amount of manganese or by controlling the temperature to which the product is heated, or by controlling the length of time that the material is heated.

As was pointed out above, substitution of beryllium in whole or in part for zinc, germanium in whole or in part for silicon, or titanium, hafnium and/ or thorium in whole or in part for zirconium,

.gives further means of changing the spectral emission characteristic of the resultant luminescent product.

I may further modify and/or control the emission spectrum characteristic by means of hightemperature quenching as described in my copending application, Serial No. 59,883, filed January 20, 1936, entitled Luminescent materials which issued as Patent No. 2,129,096 in September, 1938. By means of high temperature quenching the lattice structure of my improved crystalline material maybe expanded with a consequent shift in the emission spectrum toward the longer wave lengths. Asa result of this, additional advantages accrue to my materials and methods, since it is possible to utilize a single prepared batch of material for purposes requiring different spectral emission characteristics by the additional step of high-temperature quenching.v

In this process it willbe noted that no halides and, in particular, no fluorides are used in the process of preparing the composition. Consequently, the. necessity for providing platinum ware for use in preparation of my improved 'luminescent material is unnecessary. Therecathode ray bombardment, which has cheapness.

of preparation, controllable spectral emission,

- shall not be less than 1/10,000 or more and precise spectral emission characteristics controlled by temperature and heating process.

Consequently, my improved process and material have made possible the production of television pictures of improved quality by providing a material which can be coated on the end wall of a cathode ray tube upon which the electrooptical representation is produced, since the color of the resulting luminescence may be controlled to give-a white color of high intensity.

the spectrum, the manganese activated zinc zir conium silicate spectral emission. may be peaked .in almost any region either by heat treatment or by choosing the suitable proportions between zirconium and zinc, or the activator manganese.

' If it is desired to increase the secondary emission of this material, the manganese activated zinc zirconium silicate'which I have described, maybe mixed with small amounts of barium,

strontium, calcium, caesium, rubidium, lanthanum, cerium, thorium, any of their compounds, or other elements or -their compounds, which have large ionic or atomic radii. In certain applications of luminescent material, it is desirable to have high secondary emission and by mixing small amounts of the above identified materials; this desirable feature can be readily obtained.

Having described my invention what I claim is: 1. An inorganic crystalline luminescent material which may be represented by the general formula u(ZnO) 0(Be0) w(AO2) 25(B0a) :Mn where A is a metal of the first sub-group of the fourth vertical group of the periodic system, B is an element in the second sub-group of the fourth vertical group of the periodic system having an.

ionic radius lying between 0.8 A. and 0.! 1., and u, v, w and a: are variables such that the molar ratio of than 10,000 and the molar ratio of 1 u vandw a:

shall not be less than ,4; or more than 5.

r 2. A luminescent material comprising manganese activated zinc beryllium zirconium composition with an element in the second sub-group of the fourth group of the periodic system having an ionic radiuslying between .3 A. and 0.7 A.

3. A luminescent material consisting of manganese activated berryllium zinc zirconium silicate.

4. A luminescent material consisting of manganese activated beryllium zinc zirconium composition with an element of the second sub-a'roup' of the fourth group of the periodicsystem, and

- an alkali earth metal having a large atomic radius.

' EUMIBOIDT W. LEVERENZ. 

